Cathode-ray tube with internal cylindrical resistor between high voltage connection and electron gun

ABSTRACT

Cathode-ray tube comprising an electric resistor between high voltage connection and electron gun so as to attenuate current peaks in the case of high voltage breakdowns. The resistor includes resistance wire wound around a ceramic cylinder coaxially mounted on the electron gun.

United States Patent [1 1 [111 3,882,348 Paridaens May 6, 1975 CATHODE-RAY TUBE WITH INTERNAL [56] References Cited CYLINDRICAL RESISTOR BETWEEN HIGH UNITED STATES PATENTS VOLTAGE CONNECTION AND ELECTRON 2,829,292 4/1948 Krause 313/82 BF GUN 3,295,008 12/1966 Gallaro et alm. 313/83 X [75] Inventor: Cornelis Johannes Henricus 3,355,617 11/1967 Schwartz et a1 313/82 R Paridaens, Emmasingel, Eindhoven, FOREIGN PATENTS OR APPLICATIONS Netherlands 1,211,898 11 1970 United Kingdom 313/83 SP [73] Assignee: U.S. Philips Corporation, New

York NY. Primary ExaminerRobert Segal Attorney, Agent, or FirmFrank R. Trifari; George B. [22] Flled: Jan. 16, 1971 Berka [21] Appl. No.: 433,803

[57] ABSTRACT [30] Foreign Application Priority Data tCathOdke-rray {R136 comprising an delelctrizc resistor beween 1g v0 age connec 1on an e ec ron gun so as Feb. 21, 1973 Netherlands 7302366 to attfinuate current peaks in the case of g voltage U 8 Cl 313/450 315/3 338/302 breakdowns. The resistor includes resistance wire wound around a ceramic cylinder coaxially mounted [51] Int. Cl H011 29/96; H01 29/48 [58] Field of Search 315/3; 313/83 SP, 82 CR the Iii CATHODE-RAY TUBE WITH INTERNAL CYLINDRICAL RESISTOR BETWEEN HIGH VOLTAGE CONNECTION AND ELECTRON GUN The invention relates to a cathodeqay tube comprising an evacuated envelope, means to produce at least one electron beam, and an electrically conductive layer on an inner surface of the envelope, said means comprising a final anode, the said tube furthermore comprising an electric resistor which connects the conductive layer to the anode.

Such a cathode-ray tube is known from the US. Pat.

No. 3,295,008. It is described in said patent specification that, as a result of the high voltage on the final anode and the comparatively low voltage at the other electrodes of the electron gun, there exists a fair chance of breakdown between the electrodes. The current peaks associated therewith may have very detrimental results for the circuit of which the tube forms part, in particular in transistorized circuits. The necessity therefore exists of damping said current peaks by means of a resistor. However, said resistor should be accommodated in the tube because the envelope internally comprises a conductive layer at high voltage which has a large capacity relative to an external conductive layer. The discharge of the capacity thus formed, in the case of breakdown, must be damped by means of the resistor. The resistor should thus be connected between the final anode of the electron gun and the conductive layer, which implies that the resistor be accommodated in the tube.

US. Pat. No. 2,829,292 suggests an electric resistance layer for this purpose. However, providing an electric resistance layer with the correct resistance is very difficult in series production because the resistance of the layer is considerably influenced by the thickness thereof which shows in practice a large spreading. Moreover, it has been found that the gettering layer which is provided in the tube so as to remove the last gas residues and to bind gases which are liberated afterwards, partly lands on such a resistance layer to that the resistance layer is partly short-circuited.

The means stated in the already mentioned US. Pat. No. 3,295,008 which form an electric resistor have proved to provide insufficient protection against the detrimental results of a breakdown. Probably the field strength along the resistors described, in the case of breakdown, is still too large so that sliding sparks and the like can occur along the resistor.

According to the invention, a cathode-ray tube of the type mentioned in the first paragraph is characterized in that the electric resistor is provided on a mainly cylindrical hollow body whose axis is coaxial with the main axis of the tube. The resistor is preferably formed by a mono-layer winding of resistance wire and the cylindrical body is preferably manufactured from a material having a finite but very high electric resistance so as to prevent charging of the cylindrical body. Both during normal operation and during a possible breakdown, such a construction provides a very uniform voltage variation along the resistor. Sliding sparks are short-circuited by it and the resistor remains an effective series resistor in all circumstances between the place of the breakdown and the capacitor which discharges during the breakdown.

The invention will be described in greater detail with reference to the accompanying drawing, which shows the part of a colour television display tube relevant to the invention.

The drawing shows the glass neck portion 1 and the adjoining portion 2 of the cone of a shadow mask tube for colour television. The conical portion 2 comprises an external conductive layer 3. The conical portion 2 furthermore comprises an internal conductive layer 4 which partly extends to in the neck portion 1. ln known manner which is of no significance to the invention, a high voltage of 25 kV is supplied to the conductive layer 4 in the cone of the tube via a high voltage connection (not shown). The conductive layer 3 is connected to earth. The layers 3 and 4 with the glass of the cone as a dielectric constitute a smoothing capacitor for the high voltage.

The tube furthermore comprises three electron guns 5, 6 and 7, for generating three electron beams which each serve for the display of one colour in a manner known for shadow mask tubes. Each gun comprises a cathode, a control grid 8, an anode 9, a focusing electrode 10 and a final anode 11. During operation of the tube the final anodes 11 are at the same potential (25kV) as the conductive layer 4. This potential is supplied via a connection with the layer 4. The remaining electrodes of the electron guns are at a potential of maximum a few hundred volts which is supplied via the connection pins 12. The electron guns 5, 6 and 7 are connected to four glass supporting rods two of which are visible in the drawing and are denoted by 13 and 14. The supporting rods are secured to the connection pins 12 in a manner not shown.

A plate 15 having apertures to pass the electron beams and a sleeve 16 are welded to the final anodes 11. The electric connection between the conductive layer 4 and the final anode 11 occurs by means of the electric resistor 17 which, as already explained, is to restrict the current peaks which occur upon discharge of the capacitor formed by the layers 3 and 4 upon breakdown between electrodes of the electron gun.

The resistor 17 comprises a ceramic cylinder 18 on which a mono-layer winding 19 of resistance wire is provided. The ends of the winding 17 are connected to two contact strips 20 and 21. A few contact springs 22 and 23 which contact the conductive layer 4 which is at high voltage are also welded to contact strip 20. The contact strip 21 is welded to the sleeve 16 with a few connection strips 24 and 25. The connection strips 24 and 25 ensure both the mechanical connection of the resistor 17 to the electron guns 5, 6 and 7 and the electric connection to the final anode 11.

The length of the winding 19 is approximately 9 mm and the diameter is approximately 29 mm. The winding 9 consists of 55 turns of nickel-chromium wire in a thickness of 0.080 mm and a resistance of ohm/m. The value of the resistor 17 is approximately 500 ohm. The cylinder 18 is of ceramic material having some but very small conductibility. The resistance of the cylinder 18 is approximately 10 ohm. The conductibility of the cylinder 18 is necessary so as to prevent charging of the surface thereof. Said conductibility can also be obtained by providing the cylinder 18 with a graphite layer of very high electric resistance. It has been found in practice that the construction described damps current peaks in an effective manner in which sliding sparks along the surface of the cylinder 18 or along the winding 19 do not occur.

What is claimed is:

l. A cathode-ray tube comprising an evacuated envelope, means disposed within said envelope and including a final anode to produce at least one electron beam, an electrically conductive layer on an inner surface of the envelope,,an electric resistor which connects the conductive layer to the final anode, said electric resistor being-a mono-layer winding of resistance wire on the outside of on a mainly cylindrical hollow body said body is supported on said final anode.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,882,348 DATED May 6, 1975 |NV ENTOR(S) CORNELIS J. H. PARIDAENS It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

ON THE TITLE PAGE, Section [22] change "1971" to read -l974.

Signed and Scaled this A ttesl:

RUTH C. MA SON C. MARSHALL DANN Attestmg Officer Commissioner nj'Parenrs and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,882,348

DATED May 6, 1975 lNV ENTOR(S) CORNELIS J. H. PARIDAENS It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

ON THE TITLE PAGE, Section [22] change "1971" to read l974.

Signed and Sealed this twenty-first ,D ay Of October 19 75 [SEAL] A ttest:

RUTH C. MASON Commissioner ofPaIents and Trademarks 

1. A cathode-ray tube comprising an evacuated envelope, means disposed within said envelope and including a final anode to produce at least one electron beam, an electrically conductive layer on an innEr surface of the envelope, an electric resistor which connects the conductive layer to the final anode, said electric resistor being a mono-layer winding of resistance wire on the outside of on a mainly cylindrical hollow body spaced apart from said envelope and having an axis which is coaxial with the main axis of the tube, said cylindrical body being a material of a sufficiently low resistance to prevent surface charging.
 2. A cathode-ray tube as claimed in claim 1 wherein said body is supported on said final anode. 